Electrothermal device



Nov. 20, 1928.

O. C. TRAVER ELECTROTHERMAL DEVICE Fil ed March 11, 1925 Inventor Oliver C.Traver; by

Hi5 Attorheg.

Panama Nov. 20, 1928.

UNITED STATES 1,692,474 PATENT OFFICE.

OLIVER C. TRAVER, OF SCHENECTADY, NEW YORK, ASSIGNOR T0 GENERAL ELECTRIC COMPANY, A CORYORATION OF NEW YORK. I

' ELECTROTHERMAL DEVICE.

Application filed March 11, 1925.

This invention relates to electro-thermal devices and more specifically to electrically heated thermal responsive circuit controlling devices which are adapted to be energized by a variable or by an alternating electric current.

One of the objects of the present invention is the provision. of a simple and effective method and apparatus for heating a current conducting thermal element responsively to the variations of an electric current.

In the various forms of electro-thermal devices hitherto proposed with which I am familiar, the heating of the thermal responsive element ordinarily has been effected either by conducting or radiating heat from a suitable electric heater to the thermal responsive element or where the element is formed of current conducting material by connecting the element itself in a circuit which is arranged to be energized from a suitable source of current supply or by a combination of these methods. Although the ordinary method of heating the thermal-responsive element by conducting or radiating heat thereto may be fairly satisfactory under some conditions, nevertheless the necessity of electrically insulating the thermal element from the electrical heater requires that the element also be heat insulated from theelectrical heater to a considerable degree, and involves other structural and operating limitations that leave much to be desired. On the other hand, when the second method involving the conduction of the heating current by the thermal element itself is employed, the practical difiiculty of obtaining suflicient heating effect in the usual forms of current conductin thermal elements is encountered, particu arly when the ordinary commercial form of bi-metallic thermostatic metal having an inherently low specific resistance is used. To overcome this difliculty, it has been necessary heretofore to either employ a special high resistance bimetallic thernlostatic element, or increase the electrical resistance of the ordinary form of current conducting bi-metallic thermal element by suitably slotting'the element so as to decrease the cross sectional area as well as to lengthen the path through which the heating current flows, or to supply the thermal element with a heating current of relatively large value by connecting the element in circuit with a source of ample current gen- Serial No. 14 829.

crating capacity. However, each of these expedients leave much to be desired since special high resistance thermostatic elements are not entirely satisfactory and slotting the ordrnary thermal element is an expensive operation and also weakens the element mechanically while the provision of a source of large current generating capacity for heatmg the thermal element likewise has obvious practical limitations and disadvantages.

In accordance with my invention the current conducting thermal element is heated by directly producing the required heating current in the element itself by electromagnetic induction or transformer action. In this way the difliculties previously encountered are effect vely overcome since the relatively large heating current necessary to produce the desired heating effect is generated directly in p of bi-Inetallic thermal element becomes beneficial rather than detrimental since the value of the heating current is greatest when the resistance of the element is the lowest. In fact, a low resistance bi-metallic thermal element may be easily and efficiently heated by means of my present invention, as the heating efi'ect produced is proportional to the second power of the value of the heating current whlle the value of the heating current varies substantially inversely with the resistance of the thermal element.

For a better understanding ofmy invention, reference is had to the. following description taken in connection with the accompanying drawing which illustrates two specific embodiments of the invention for the purpose of explaining the principles thereof and 1n which Fig. l is a side view partly in section of a thermal responsive circuit controlling device embodying the invention; Fig. 2 1s a more detailed view showing the arrangement of the thermal responsive element employed in the device shown in Fig. 1; Fig. 3 shows a modified arrangement of the thermal responsive device; and Fig. 4 is a top view of the device shown in Fig. 3 with certain parts omitted.

The novel features and combinations which I believe to be characteristic of my invention are pointed out with particularity in the appended claims.

Referring to Fig. 1, it will be seen that the thermal responsive circuit controlling device illustrated comprises a current conducting thermal responsive' movable element 10 formed of the ordinary type of bi-metallic thermal metal having both current conducting and magnetic properties. The bi-metallic element 10 is secured at one end to the magnetic member 11 by means of the screws 12, and carried at its free end the movable circuit controlling contact 13 which cooperates with the stationary contact 14. As more clearly shown in Fig. 2, the thermal element 10 is formed as a winding in the shape of an annulus or elongated ellipse so as to constitute a single turn closed electrical circuit, although it will be evident that the element may be formed in a winding of other shapes if desired. The magnetic member 11 extends loosely through the aperture in the thermal element 10.

In order to heat the thermal element 10 by electro-magnetic induction or transformer action in accordance with my invention, an energizing windin 15, which may be of the usual type adapte to be energized by alternating current, is disposed in mutual inductive relation with the winding or single turn closed circuit formed by the element 10. It will be observed that in the device illustrated a substantially closed magnetic circuit is provided for the flux of the energizing winding 15 by the magnetic member 11 and the U-shaped frame 16 which is of magnetic material and serves to inductively interlink the energizing winding 15 and the winding or single turn closed circuit formed by the thermal element 10. The frame 16 is suitably secured to the upper end of magnetic member 11 with a non-magnetic washer or spacer 17, preferably of insulating material, interposed between the member 11 and the frame 16 and a screw thread plug 18 of magnetic material is adjustably mounted in the bottom leg of frame 16 to permit the reluctanceofthemagnetic path for the flux of winding 15 to be varied. Preferably, the cooperatlng ends of plug 18 and magnetic member 11 are chamfered, as indicated in the drawing, and a small connecting pin 19 of magnetic material may be provided for insuring that the variation of reluctance is effected gradually upon adjustment of the plug 18. The lock nut 20 is provided for securing the plug 18 when the proper adjustment is obtained.

It will be evident that while the magnetic member 11, frame 16, plug 18, and connecting pin 19 constitute a ma netic structure having a substantially close path for the flux of energizing winding 15, nevertheless the washer or separator 17 of non-magnetic material serves-to form a pair of magnetic poles in the structure which are disposed in attractive relation with the free end of the bi-metallic thermal element 10 as shown in the drawing.

A pole piece 2Lmay be adjustably mounted in the frame 16 as shown in order to permit variation of the magnetic attraction of the free end of element 10 if desired.

As thus constructed and arranged the operation of the circuit controlling device shown in Fig. 1 is as follows: Upon the energization of winding 15 from a suitable source of alternating current, an alternating flux is set up in the magnetic structure composed of member 11, frame 16, plug 18 and connecting pin 19. In accordance with the well known law of mutual electric magnetic induction this alternating flux induces an alternating voltage in the closed circuit formed by the thermal element 10 which causes an alternating current to circulate in the closed circuit formed by the element.

The value of the current induced in the thermal element 10 upon energization of winding 15 from an alternating current source varies inversel with the resistance of the element and is o relatively large value since the ordinary type of bi-metallic thermal metal composing the element 10 has inherently low resistance. As the lar e heating current circulates in element 10, t e temperature thereof is increased under certain conditions. The iron losses in the magnetic circuit including the magnetic member 11 also serve to increase the temperature of thermal responsive member 10. The resulting fiexure of the element moves the contact 13 towards the stationary adj ustable contact 14. As the movement of element 10 continues responsively to the increase in temperature thereof, the free end of the element is brought within the stronger portion of the magnetic field of the oles of the electromagnet formed by winding 15 and the magnetic structure comprising frame 16, pole piece 21 and magnetic member 11. The resulting attraction of element 10 serves to effect the operation of the contacts 13 into circuit closing engagement with the contact 14 with a snap action. It will be understood that, while not shown, a holding winding for maintaining the contacts 13 and 14 closed may be provided if desired, and that suitable inertia or other damping means may be used to prevent object-ionable oscillation of 10.

It will be evident that the heating of element 10 required to flex the free end thereof into attractive relation with the pole" piece 21 varies with the degree of energization of winding 15. With low energization of winding 15, an appreciable heating of element 10 is necessary while with increased energization of winding 15, the magnetic attractive effect is greater and consequently a smaller increase in temperature of element 10 serves to flex the free end thereof into attractive relation with the pole piece 21. With an extremely heavy energization of winding 15, the attractive elfect upon element 10 may become sufficient to cause practically instantaneous operation thereof to close the contacts 13 and 14 before any appreciable heating of element 10 occurs. 1

- Upon the de-energization of the winding 15 in the arrangement shown the free end of element 10 is no longer attracted and the temperature of the element starts to decrease since the heating current also stops. Thereupon the free end of element 10 carries contact 13 out of circuit closing engagement with the contact 14 and the subsequent cooling of the element returns the contact 13 to the position in which it is shown preparatory to a subsequent operation of the thermal device in the manner previously described upon reenergization of the winding 15.

Variation of the value of the energizing current of winding 15 necessary to effect operation of thermal element 10 is easily obtained by adjusting the plug 18 so as to vary the reluctance of the magnetic path for the flux of winding 11. When the plug 18 is moved away from member 11 so as to increase the reluctance of the magnetic circuit, the value of the energizing current of winding 15 required to effect operation of the element 10 is increased and when the plug 18 is moved towards the member 11 so as to decrease the reluctance, the value of energizing current iscorrespon'dingly decreased. It will be evident that adjustment of plug 18 varies the magnetic attraction of the free end of thermal element 10 as well as the heating current induced in the element and thus varies the temperature to which thermal element 10 must be raised to effect closure of the contacts 13 and 14.

While not shown in the drawing, it will be understood that the cooperating contacts 13 and 14 may be connected to control the circuit of an electrically operated device such as a switch or conductor in order to efl'ect the operation of the same responsivelv to operation of thermal element 10. Furthermore, it

will be understood that winding 15 may be designed to have a current carrying capacity of any value that may be desired. Thus the energizing winding 15 may be arranged to be connected to power circuits of small or large current capacity and the thermal device embodying my invention may be arranged in any suitable manner to provide overload protection to the circuits, or to perform other desired circuit controlling service.

The modified form of thermal responsive device embodying my invention, shown in Fig. 3, has the same general structural and operating characteristics as the thermal de vice described in connection with Fig. 1. It will be observed, however, that in the modified form, the thermal element 10 is mechanically secured at one end to the magnetic member 22 which is suitably mounted upon one end of the magnetic member 23 and c0- operates with the U-shaped magnetic member 24 which is secured to the other end of magnetic member 23 to form a substantially closed path of magnetic material for the flux of energizing winding 15. The flux path, however, is interrupted by the air gap between the magnetic members 22 and 24. The thermal element 10 is formed in a rectilinear shape, as more clearly shown in Fig. 4, and the free end of thermal element 10 carrying the contact 13 is arranged to move in the air gap between the magnetic members 22 and 24.

Although not shown in the drawing, it will be understood that suitable means for varying the reluctance of the flux path of winding 15, similar to the plug 18 described in connection with Fig. 1, may be provided if desired.

The operation oft-he device shown in Fig. 3 is as follows: Assuming the temperature of thermal element 10 to be at the normal value 1 at which the free end of the element is flexed to move the circuit controlling contact 13 to the open circuit position in which it is shown, energization of winding 15 from a suitable source of alternating current serves to set up an alternating flux in the substantially closed magnetic path formed by magnetic members 22, 23 and 24 which generates aheating current of large value in the closed circuit formed by thermal element 10. The resulting heating efi'ect raises the temperature of element 10 and the free end thereof is gradually flexed so as to move the contact 13 toward the cooperating stationary contact 14. As the end of element 10 moves upward in the air gap between the magnetic members 20 and 22, the magnetic attractive eflect upon the end of element 10, as well as the motor effect produced by the reaction of the current flowing in element 10 upon the magnetic flux in the air gap, increases until finally the end of element 10 is quickly moved to carry the contact 13 into circuit closing engagement with the contact 14, thus closing the auxiliary circuit controlled by the thermal responsive device in an obvious manner.

The return of thermal element 10 and contact 13 to the position in which they are shown in the drawing is effected upon the de-energization of winding 15 in an obvious manner.

In accordance with the provision of the patent statutes, I have described the principle of operation of my invention, togetherwith the apparatus which I now consider to represent the best embodiment thereof but I would have it understood that the apparatus shown is only illustrative and that the invention may be carried out by other means.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. An electro-thermal device comprising a current conducting thermal responsive elementin the form of a winding and an energizing winding disposed in mutual inductive relation with said first'winding for inductively producin a flow of circulating heating current in the element.

2. An electro-thermal responsive device comprising a current conducting movable thermal responsive element in the form of a single turn closed circuit, an ener izing winding, and a magneticcircuit inter inking said energizing winding with said single turn closed circuit formed by the thermal element whereby the thermal element is heated in accordance with the current induced therein responsively to variations in the energization of said winding.

3. An electro-thermal responsive device comprising an energizing winding and a current conducting movable thermal responsive element electrically disconnected from said winding and forming a single turn closed circuit in mutual inductive relation with said winding whereby the element is heated by the current induced therein responsively to variations in the energization of the said winding.

4. An electro-thermal device comprisin a current conducting thermal responsive e ement having an aperture therein, a magnetic member extending through the aperture in said element, and an energizing winding for producing a variable flow of flux in said magnetic member to thereby induce a flow of current in said thermal element for heating the element.-

5. An electro-thermal device comprising a current conducting thermal element having an aperture therein, an electromagnet having a portion of the magnetic circuit thereof extending through the aperture in said thermal element for inducing a heatin current in said element responsively to variations in the energization of said electromagnet, and means for varying the reluctance of said magnetic structure to control the heating of said thermal element.

6. A thermal electric circuit controlling relay comprising a current conducting thermal responsive movable element having an aperture therein, an electromagnet disposed in attractive relation with said element and having a portion of the magnetic structure there of extending through the aperture in said element for producing a flow of current therein upon variations in the energization of said clcctromagnet, and means for varying the reluctance of the magnetic structure of said elect romagnet to control both the attraction of said thermal element and the heating thereof.

7. An electro-thermal responsive device comprising an energizing winding, a magnetic structure for the flux of said winding, current conducting thermal responsive means associated with the flux of said structure to be heated responsively to the current induced in said means upon variations in the energizing current of said winding, and means for varying the reluctance of said magnetic structure to control the heating of said element.

8. A thermal electric circuit controlling device comprising current conducting thermal responsive means, switch mechanism arranged to controlled by said means responsively to variations in the temperature thereof, means for producing a flow of heat 1ng current in said means comprising an energizing winding inductively related with said means, and an adjustable magnetic member for yaryin the inductive relation between said win mg and said means to control the variation in temperature of said means upon variation in the energizing current of said winding.

9. A thermal electric circuit controlling device comprising current conducting thermal responsive means, switch mechanism arranged to controlled by said means responsive to varlations in the temperature thereof, means for inducing a flow of current for heating said thermal responsive means comprising an energizin winding and a magnetic structure there or having a magnetic member adjustable along the axis of said winding for varying the value of the current induced for heating said thermal responsive means upon variation in the energizing current of said winding.

10. A thermal electric device comprising an energizing winding, a magnetic structure therefore, having magnetic poles, a thermal responsive element of magnetic material disposed in attractive relation with said poles, and a closed circuit disposed in inductive relation with said energizing winding and includlng said thermal responsive element, whereby the said element is operated by both the magnetic attraction of said poles, and the induced current flowing therein upon variations in the energization of said windmg.

11. A thermal electric device comprising. an energizing winding, a magnetic structure therefore having poles, a current conducting thermal responsive element disposed in the magnetic field of said poles, and in inductive relation with said winding whereby the said element is operated responsively to the heating efiect of the current induced therein and to the motor effect between the current in said element and the magnetic field of said structure.

12. A thermal electric circuit controlling relay comprising a current conducting thermal responsive movable element having an aperture therein, an alternating current electromagnet disposed in attractive relation with said element and having a portion of its magnetic structure extending through the aperture in said thermal element, means for securing one end of said thermal element in heat conduction relation with said magnetic structure, switch mechanism arranged to be operated by the free end of said thermal element and means for controlling the flow of flux through the magnetic structure of said electromagnet and thereby vary both the magnetic attraction of said element and the heating thereof upon a predetermined energization of said electromagnet.

13. An electrically actuated, thermo-responsive device including a transformer having a primary winding adapted to be energized by the circuit current, and a closedcircuit secondary winding, constituting a thermo-responsive element.

14:. An electrically-actuated, thermO-responsive device including a transformer having a primary winding adapted to be energized by the circuit current and a closed-circuit secondary winding constituting a thermo-responsive element, the primary winding having a greater number of turns than the secondary winding so that the current in the thermo-responsive secondary winding is greater than the circuit current.

15. An electrically-actuated, thermo-responsive device including a transformer having a primary winding adapted to be energized by the circuit current and a closed circuit secondary winding constituting a thermo-responsive element, and means controlled by said thermo-responsive element.

16. An electrically-actuated, thermo-responsive device including an expansible thermo-responsive member having a fixed end and an end free to move due to expansion and contraction of said member, means electrically connecting said fixed and free ends, and means to set up a magnetic flux cutting said member in a direction to cause an induced current to flow through said member and said connecting means, whereby to heat and expand said member.

17. An electrically-actuated, thermo-responsive device including a transformer having a primary winding adapted to be energized by the circuit current, a secondary winding comprising an expansible thermoresponsive member having a fixed end and a free end arranged for movement in response to expansion and contraction of said thermoresponsive secondary winding, and means to connect said ends electrically.

In witness whereof, I have hereunto set my hand this th da of March, 1925.

0L VER C. TRAVER. 

